Balancing duplex circuit



1 I w. D. BUCKINGHAM 2,186,006

- BALANCING DUPLEX CIRCUIT Filed Sept. 27, 1935 3 Sheets-Sheet 1 LINE F|G.2' FIG.3 FIG.4 FIG; 5

A c I D E PIC-3.6

c {9 F G I H I J F|G.7 FIG-.8 F|G.9

INVENTOR W. D., BUCKINGHAM.

AT ORNEY J 9, 1940- i w. D. B UCKINGHAM v ,186,00

' BALANCING DUPLEX 011100.11

Filed Sept r 27, 1935 3 Sheets-Sheet 2 LINE IOl

FIGQ'II INVENTOR W.D. BU CKINGHAM ATTO NEY Jan. 9, 1940- w. D. BUCKINGHAM BALANCING DUPLEX CIRCUIT 3 Sheets-Shet 5 Filed Sept. 27, 1935 AMPLIFIER FIG. l4

FIG, I5

M m Y m W MR we mam Y v Patented Jan. 9, 1940 I UNITED STATES. PATENT OFFICE 81.1mm... N. Y.

, assignor to The Western Union Telegraph Company, New York, N. 1., a corporation of New York N Application September 34 Claims.

This invention relates to the balancing of signailing circuits and the like, and'more particularly to a method of and means for indicating, analyzing and correcting unbalanced conditions in electrical circuits or apparatus more rapidly and with a greater degree of accuracy than has been obtained heretofore in practice.

The primary object of this invention isto provide an improved and more accuratexmeans of detectingand locating unbalance in circuits such as duplex signalling circuits, and a method of employing such means which may form the basis of a new technique in the balancing and use of such circuits for telegraph or other types of signals because of the greatly improved balance that maybe effected and maintained by utilizing this method.

,As is well understood in the art, a duplexed signal circuit is one arranged so that messages or signals may be transmitted in both direc-' 4 by differentiation or the'use of a bridge circuit arrangement into equal or proportional parts and providing an artificial line simulating the :actual line or conductor so thatthe propagation of a signal wave through the actual line and the artificial line is substantially the same. When this condition obtains for the bridge circuit arrangement,-a receiving instrument across the conjugate points of the bridge will not be affect- -ed by the outgoing signals. However, if the char- 0 acteristics of the artificial line do not match those of the real line, the propagation of such signal current is not equal at all instants in the signal cycle, and the unbalanced condition will cause a flow of current across the bridge. Corresponding disturbances would occur in diflerentially duplexed circuits.

As is well known, duplex operation of the signal circuit may be applied either to land lines or to ocean cables. In the latter instance, because of the small current used and the changing conditions to which the cables are subjected, the problem of-obtainingand maintaining approximate balance is extremely difflcult.

Although artificial lines are constructed according to mathematical calculations, they 27, 1935, Serial No. 42,500

nevertheless only an approximation of the real line and considerable manipulation'and adjustment of'the' artificial line is necessary before a 'working balance, particularly in a cable circuit, can be established. Such a balance is not permanent because of widely varying conditions which afl'ect the electrical properties of cables of great length submerged beneath the surface of the seas, and frequent readjustments of the artificial line are necessary. In the earlier stages of the art of duplex circuits, particularly as applied to cables, the obtaining of a balance was a long and tedious process, primarily because of the fact. that no reliable means of indicating the a exact conditions of unbalance were available.

The state of balance between the cable and the artificial line was then judged entirely by the performance of the relay and receiving apparatus which by their very nature were designed to be insensitive to unbalanced conditions. In an eflort to show more clearly the actual un-- balanced conditions a string os'cillogra'ph method of picturing the unbalance has been employed. This expedient, however, represented only a slight improvement over the previous methods because ofthe lack of sensitivity of the instrument, the time delay in obtaining the oscillographic picture and the difiiculty in interpreting such a picture in the terms of position and sense of the unbalanced portion of the artificial line. According to this invention'apparatus is provided for picturing or forming a steady and continuous patternvortime-current graph of the unbalanced condition which represents the relative instantaneous values of the current propagation in the actual and artificial lines or other elements to be balanced throughout the entire signal cycle -or any desired portion thereof. Ac-

cording to this invention this pattern not only shows the instantaneous values just referred to, but by an easy, rapid and continued interpolation, the sense or type of unbalance, together with an accurate location of the points of unbalance in the artificial line for all portions of the artificial circuit may be obtained. 1 A further feature of the invention involves a new method and technique of rapid and accurate balancing of electrical elements, such for example as duplex circuits, of which the cable circuit is the most complicated type.

It is an object of this invention, therefore, to devise a method with the use of appropriate improved. apparatus herein described, for obtainins within a relativelyshort space of time a higher degree of accuracy of balance or simulation at all points between the'actual and artificial line of duplex circuits.

It is a further object of this invention to devise a method for obtaining a more accurate balance in a signalling circuit in order that a working balance may be maintained for a longer period of time than has been possible heretofore.

Another object of the invention is to provide apparatus which will indicate unbalance with great accuracy, thus eliminating uncertainty in the determination of the same.

Another object of the invention is to provide means for indicating unbalance in such a manner that it may be easily read and interpreted and further to provide means which will give a sustained indication from recurring signals.

' -A further object of the invention is to'provide means for indicating at the same time the position, the nature, and the direction of unbalance.

A further object of the invention is to provide means which will detect and indicate whether the unbalance is inductive, capacitative, or resistive.

A further object of the invention is to provide means for indicating quickly and accurately the efiect of a correction made in the artificial line in an attempt to establish accurate balance.

A further object of the invention is to provide means to give a visual graphic representation of the relative propagation of a signal wave or any desired portion thereof over the actual'and artificial lines.

A still further'object of the invention is to provide means for forming a symmetrical pattern representing the unbalance current whereby parasitic currents flowing through the line or dicating device embodying features of thepres-v ent invention; 7

Fig. 2 illustrates the theoretical wave form of a cable reversal;

Fig.3 is apattem produced on the screen of the cathode ray tube when there is no unbalance between the real and artificial line;

Fig. 4 is a pattern produced by an excess of capacity-in the middleand distant end of the artificial line;

.Fig. 5 is a pattern produced by an insufiiciency of capacity at the middle and distant end of the artificial line;

Fig. 6 illustrates patterns produced by an actual artificial line having excess capacity introduced at various points therein;

Fig. '7 illustrates patterns produced by an actual artificial line having insuflicient capacity at various points therein;

Fig; 8 illustrates a pattern produced by excess .capacity near the head end of the artificial line and'an insufilcient capacity near-the opposite end;

Fig. 9 illustrates a pattern produced by anexcess of resistance near the head end of the artificial line; I

Fig. 10 is a circuit diagram of a brid e type :duplex'circuit having a modified balance indicating device associated therewith;

Fig. 1. ra'tely at each end, it is only 11 for purposes of illustration to deal with theapparatus Fig. 11 illustrates patterns produced with the arrangement of Fig. 10 when excess capacity is introduced at various points in the artificial line;

Fig. 12 illustrates patterns produced by capacity unbalance occurring at two spaced points along the artificial line;

Fig. 13 illustrates patterns produced by resistance unbalance alone and resistance and capacity unbalance;

Figs. 14 and 15 illustrate other patterns resulting from unbalance and disturbances in the line or cable; and

r Fig. 16 is a circuit diagram of a modified system arranged to indicate unbalance while the line or cable is in use and printing or other signals are being transmitted thereover.

It has been found in accordance with this invention that the cathode ray tube when provided with suitable associated circuit apparatus, such employment of this method a rapidity of attainment of balance together with a greater degree of accuracy than previously known inthe art has been obtained. v

A vacuum tube amplifier may also be employed as a part of the test circuitapparatus and may be coupled between the cathode ray tube and the signal circuit for amplifying the unbalance potentials. It is particularly useful as the refinement of the balance proceeds in amplifying the small remaining unbalances in such a manner as to make them stand out in the screen pattern, thus facilitating the determination of the adjustment required in the most diiiicult part of the balancing procedure where the adjustments are critical v and of exceedingly small values. 1

Three embodiments of apparatus associated with the cathode-ray oscillograph for carrying.

out the improved method of balancing according to this invention as applied to duplex signaling circuits will bedescribed herein. It is to be understood, however, thatthe invention is not limited to such application orthe particular apparatus described. For a complete understonding of the invention Figs. 1 and 10 may be considered somewhat complementary to each other.-

Fig. 10 is explained by reference to Figs. 11 to 15.

A cathode ray tube and associated apparatus required for the balancing of a simple differential duplex circuit will now bedescribed, reference being had to the diagrammatic illustration of Since duplex circuits are balanced sepaat one end of the line only and thedraw'ings are accordingly so restricted. The apparatus at one end of the line comprises a source of positive potential III, a source of negative potential II, and a key l2 for alternately connecting positive and negative potential in the circuit; The key l2 may be operated either manually or mechanically (as hereinafter described in connection with. Fig. 10) For balancing operations the key may be operated continuously to impose a continually the real and artificial lines. The tube is prefersource of unbalance potentials.

ably connected so that the propagation of the signals along the real line produces a horizontal sweep of the electron stream or light spot on the screen, and the unbalance potentials across the receiving or recording device I 4 produce vertical deflections or deflections laterally of the normal axis of the screen pattern. The preferred form of the cathode ray tube is the type in which the electron beam is deflected or controlled by potentials imposed upon quadrant plates 2!, 22, 23 and 24.

In actual use an amplifier will usually be connected between the cathode ray tube 20 and the This has been omitted in Fig. 1, however, for the sake of simplicity and theplates of the cathode ray tube have been connected directly to the circuit. [in amplifler similar to that to be described in connection with Fig. 10 is preferred.

The cathode ray tube, as is well known by those skilled in the 'art, comprises a pear-shaped glass vessel having a luminescent screen which may be formed upon the substantially flat-end surface upon which an electron beam impinges. For the purposes of this invention the flattened end surface is preferably provided with a retentive screen, such that a. sustained pattern. will be formed upon the screen so long as the recurring signals sent out over the line produce the'same trace. A fluorescent and phosphorescent screen of the highly retentive type, such as calcium fluoride, upon which the patterns will be retained for as much as thirty to forty seconds, is preferred. A screen of this character is disclosed 'int the patent to Du Mont No. 2,000,014, dated May '7, 1935. As will appear further on in the description, with a highly retentive screen, changes produced by balancing adjustments may be caused to throw a new pattern upon the screen before the old pattern has faded out, which is extremely useful for comparative diagnosis of the effect of balancing manipulations.

Plates 2| and 23 of the cathode ray tube 20 which produce the sweep or horizontal displacement of the electron beam, are connected across the coil iii 'of the differential relay by conductors 25 and 26, respectively. The coil l5 carries the signal current to the real line and the potential drop across this coil is employed to provide the source of sweep circuit potential. The plates 22 and Mare connected across the conjugate points of the relay by the conductor 25 extended, and

conductor 21, so that unbalance voltages appearing between the real and artificial lines produce displacements of the electron beam away from the normal axis. r

The voltage drop across the coil 15 impressed upon the plates 2| and 23 sweeps the electron plates illustrated as exactly like that going to the real line.

beam across the screen in a straight line along gwhatmay be termed the axis of the screen when there is no unbalance-in the circuit. However, if any unbalance voltages exist, the electron beam or spot of light onthe screen will be deflected up and down by an amount proportional to the unbalance. Thus, as the spot is being swept from side to side by the line alternations, it simultaneously moves up or down to produce humps, so to speak, on the horizontal line, the. height and shape of these humps indicating the amount and sense of the unbalance, while their positions on the horizontal line indicate the places in the signal cycle where the unbalance occurs. Since the propagation of the signal current is consonant with the signal cycle, the positions in the signal cycle correspond relatively to the place or the middle section of the lines correspond to the middle part of the cycle pattern, and the end sections of the lines correspond to the-last part of the cycle pattern. It is the employment of the cathode ray tube in the manner set forth by this invention that changes the problem of balancing duplex circuits from a hit-and-mlss procedure to a more exact science. This feature is important because not only the amount of the unbalance, but also the direction ofthe unbalance and its position in the artificialllne are indicated.

Since the matter of balance is 'morecritical and more difficult to obtain in telegraph circuits and particularly'cable circuits, the operation of the test apparatus is described as applied to the latter.

The method or technique of balancing a cable by the apparatus devised and employed according to each embodiment of this invention can best be explained and illustrated by an explanation of the types of patterns produced upon the screen of the cathode-ray tube when a series of known conditions of unbalance are produced. By first ascertaining the significance of the shape and. form of the patterns representing different kinds of unbalance, the amount and type of unbalance of an actual artificial line can readily be arrived at from the pattern produced-thereby. v

Referring to Fig. 2, the theoretical shape of a complete cycle of a singal current wave is illus- ,more distant sections of the line have their capacities separated from the head of the cable by the cable resistance and so are slower in taking their charge, causing the cycle portions lr-c-d-e to slope gradually downward toward the'axis of the curve. At e battery is again reversed and the current drops rapidly to j duplicating a-b in the reverse direction. From I. the current curve slopes again through -g-h-d to a point corresponding to the initial point a, completing the cycle. a In balancing a duplex circuit the problem is to make the current wave going to the artificial line This means that the section t---b of the current wave 1 the artificial linewhile the sections b-'-cd-e respectively must be matched by adjustmentsin the middle and toward the end of the artificial line.

As is well understood, an artificial line is generally composed of sections of capacity separated by resistances and sometimes inductances, the capacity condensers simulating the cable or line capacity-andthe resistors and inductors simulating the line resistance and inductance and producing a' similar delayed charge efiect. The sections of the artificial cable near the front correspond to the head of the real cable and the middle and lastsections oi the artificial line correspond to the middle and far end of the real cable or'line.

The visible patterns on the screen of the cathode-ray tube will vary in accordance with the relation betwen the characteristics of the real and artificial lines. If there is no unbalance the pattern will be a straight line as shown in Flg. 3, because of the fact that the only voltages applied to the quadrant plates will appear between the horizontal plates 2| and 23, since there is no potential diflerence between the points-X and Y of Fig. 1 throughout the complete signal cycle. At the pont a in the signal cycle, as shown in Fig. 2, the spot of light upon the screen produced by the electron beam will appear at point a on the pattern o1v Fig. 3. As soon as the battery is reversed and positive potential is applied, the plate 23 of the tube becomes more positive due to the drop across the coil IS in the upper arm of the relay causing the spot to travel rapidly to the right and assume the position represented at D. From the position b the spot will travel more slowly from right to left as the current curve drops to position e in Fig. 2 forming the portion of the pattern b-c-d-e.

It will be readily understood that where the beam travels rapidly thetracing uponthe screen will be dim and where the beam travels more slowly the tracing will increase in brightness.

In order to illustrate this the width of the theoretical trace increased from b to e as will be seen by referring to the pattern. At e on the signal cycle battery is again reversed and negative potential applied, causing the current curve to drop rapidly from e to f '(Fig. 2). On the pattern the beam will swing rapidly to the left from. e to I. From this point as the current curve slowly rises following the line fdha indicated in Fig, 2 .the spot of light produced -by.the beam will travel toward the right from I through g-h to a. From the latter indications given in the theoretical pattern the form of the portion oi the pattern corresponding to the various portions or the current curve can be readily identified. For each signal cycle the spot 01 light will move across the oscillograph screen in the manner just described. The screen retains the image so that the recurring movement of the spot will produce what appears to be a complete sustained pattern on the screen.

For a condition of unbalance the pattern upon the screen will be distorted from that shown in Fig. 3, the shape being determined by the amount and position of the unbalance between the real a- -b-c but that after that the artificial line the real line.

I less current due to the insufficiency of its ca-- takes more current than the real cable due to the'iact that the capacity in the remote part of the artificial line is greater thanthat oi the remote part of the cable. The pattern upon the oscillograph would then look like that illustrated in Fig. i. From a to b and from]; to c the drop across the coils I 5 and l6 0! the relay at the sending end would be equal and the potential at the conjugate points X and Y would be the same. However, from c to d and d to e the artificial line would take more current than This would-cause the drop across coil It to be greater than that across coil I5 making. the lower plate 2| connected .to the upper conjugate point X more positive than the upper plate 22 connected with the lower conjugate point Y. This would cause the spot of light to swing. downwardly giving the dropping portion of the pattern from c to e as illustrated. The pattern for the other haliof the cycle would be a duplication 01' this in the reverse order.-

If the opposite conditions are assumed, that is, a condition in which-the artificial line takes pacity at the remote end, a pattern of the opposite form will beproduced such as is illustrated in Fi 5.

Now with the theoretical patterns in mind .attention is directed to'the screen patterns produced by actual conditions. Referring to Figs. 6', 7, 8 and 9, there are shown tracings 01' photograps of the actual screen patterns produced by apparatus set up under known conditions and in which certain known factors unbalanced the artificial line.

In Fig. 6 a series of tracings A, B, C, D and E illustrate the patterns produced when a circuit is set up with a condition of good balance existing between the main and artificial lines and in which a known excess capacity is introduced at 'unbalance. Tracing A shows a'condition of good balancein which the tracing appears as a substantially straight line of a tapering character simulating the theoretical illustration of Fig. 3. This condition'was then changed by the .addition of a small capacity at the remote end of the artificial line, causing. the artificial line to drawv more current than the real line at the end of the cycle. This produced the pattern form B and corresponds to the supposed theoretical condition illustrated mm. 4, in which the inner ends are displaced from the horizontal in what might be termed'a clockwise direction. As will be remembered the outer or slender portion of the pair'oi streaks or images on the pattern represents the near or head end 01' the line. These are offset somewhat dueto the reflex o! the unbalance at the end of the cable.

Pattern C is a tracing of the Dattem produced when the excess capacity is moved to a point inwardly from the remote end. Here it is seen that the humps or displacements appear back from the inner end of the images at about the points d and h permitidng the ends e and a to aline themselves substantially on a horizontal line. This indicates that the signal lines are substantially in-balance at theremote end but are unbalanced at a small distance inwardly from the remote end.'

The pattern D resulted when the artificial line excess capacity was moved inwardly a step further and placedat a point between its effective center and head end. It will be noted that the inwardportions. e and a of the tracings remain 40 various points in the artificial line producing an centered along a substantially horizontal line while the outward portions b and 1 representing the parts approaching the head end are further displaced but still retain an inward curvature at their outer ends. This indicates that the unbalance instead of being at the head end is some distance therefrom.

The pattern E resulted when the excess of the capacity of the artificial line was moved to a point substantially at the head of the artificial line. In this tracing the inward ends e and a representing the condition of balance at the distant end of the artificial line remain in substantially horizontal alinement. However, the curvature of the tracing at the outer ends b and f is considerably less and does not incline back toward the center indicating that there is a section adjacent the head of the artificial line which is in substantial balance with the real line. It

is to be noted that these tracings represent a condition in which there is too much capacity in' the artificial line, and that for such a condition the image at the right of the screen pattern which represents the positive half of the signal cycle falls below the horizontal line.

In contrast to the above described condition. Fig. '7 represents tracings of photographs of the cathode-ray screen pattern when capacity is removed from the artificial line, or in other words,

a condition in which the artificial line is deficient in capacity at some point.

Referring to tracing F, a small amount of capacity was'removed from the front end of the artificial line to produce the tracing shown. It will be noted that the tracing represents a condition substantially opposite that represented by V head end or the line was restored and asmall capacity removed from the middle of the artificial line. This introduces a curvature in the images near the center thereof. The hump in the right image is above the horizontal line and in the left,

of course, below. The tracing H was produced with a condition of insuflicient capacity at the end of the artificial line. It will be noted that this is substantially-the reverse of tracing B in Fig. 6. The curvature is moved outwardly toward the end of the figures while the inner ends appear somewhat displaced in the opposite direction indicating a similar reflex condition.

. It will be noted that the unbalance conditions as illustrated in Fig. 6 represented four steps of change from one end of the artificial line to the other-while those illustrated in Fig. 7 represented three steps of change. From a comparison of the tracing images in both figures it will be readily seen that they indicate not only an approximation' of the amount of unbalance but also the position and the sense of the unbalance.

of capacity at that point.

tracing images are formed as the previously described tracings would indicate. Specifically, the right image has its outer or thin portion b which represents the head of the artificial line, curved or bowed downwardly, which is the direction to be expected for excess capacity, at the head end of the artificial line asindicated by the tracings D and E in Fig. 6. 0n the other hand the image is formed with an upward hump or curvature adjacent the inner end e, indicating a deficiency This portion of the image corresponds to the tracing H, in Fig. 7, except in the latter tracing the, deficiency was right at the tail of the artificial line whereas in the present case the deficiency was at a point slightly removed from the tail of the artificial line. A better indication of the formations is probably obtainedby referring to tracing C of Fig. (i in whichthere is only one condition of unbalance and at a point removed-from the tail, of the artificial line, and in the opposite sense, that is, a condition or excess capacity rather than a deficiency. It will be seen that the hump near the inner. end of the images extends in the opposite direction. i

The tracing illustrated in Fig. 9 represents condition in which the relative propagation of the signalalong the real and the artificial line is substantially the same, but at some point adjacent the head of the artificial line there is too much reaction produced by the presence of an excess amount of resistance. Such a condition causes a vertical displacement of the images on a screen as shown in the tracing. It will be noted that the shapes oi the images are substantially straight or horizontal and in this respect the images are quite similar to those illustrated in tracing A, Fig. 6. The difierence between the tracings is evident as a vertical displacement.

Another form of this invention which gives a difierent graph pattern is illustrated in Fig. 10. It operates on somewhat different principles from the embodiment just described, differing primarily in the sweep circuit, the control potentials for which are not produced bythe signals themselves, but by separate means timed and phased in accordance with the signals. Preferably the arrangement is such that the pattern upon the'cathode-ray tube screen is extended'the full width 01' the light spot or electron beams sweep for each haliof the signal cycle, thus enabling the deflections or humps in the pattern to be outlined in greater detail. While more apparatus is required in accordance with the embodiment now'to be described, the interpolation of the unbalanced conditions in terms of artificial line'adjustment 'isgreatly facilitated and the symmetrical, pattemJormed .in the screen has other advantages as will be pointed out."

The illustration in Fig. 10 shows the apparatus in greater detail than the illustration employed in connection with the previously described embodiment. Appropriate parts of the apparatus here-described such as the amplifier, may be incorporated in theprevious embodiment. One side of the duplex network embodies a real line or cable ill which may be any type of duplexed land line circuit or any type of duplexed cable circuit, either long or short, loaded or unloaded,

or the combined type-of cable, several of which have been laid in late years, comprising a loaded central section and non-loaded end sections. The other side ofthe'duplex' network comprises a suitable artificial line or-c'able 3| capable of ad- 'justment. The cable and artificial line are con- 15 will presently be described.

nected through a network 32. The unbalance voltages are impressed upon the cathode-ray tube 33 through an amplifier 34. A commutator device 35 is employed for coordinating the genere ation of test signals and sweep circuit potentials.

The commutator is illustrated in developed form. It comprises three rings 36, 31 and 36, swept by a brush arm 39 having separate brushes 4|, 42 and 43 corresponding respectively to the rings 36, 31 and 38 and each insulated from the others. The brush 4| sweeping the commutator ring 36 is connected through conductor 44 to the duplex network 32 for impressing the test signals thereon. The brushes 42 and 43 are connected to conductor 45 providing one side of a shortcircuiting arrangement, the function of which The ring 36 is divided into an evennumber of segments. In the illustration it comprises four segments, 46, 41, 43 and 49. Alternatesegments are connected to sources of opposite potential,

signal cycle will have been completed when two.

complete consecutive segments of the ring have been passed over by the brush.

The other two rings 31 and 36 of the commutator embody short segments which when engaged by the brushes 42 and 43 provide a shortcircuiting means for the sweep circuit of the tube 33 as will presently be described. The ring 31 embodies a first segment 52 and a second segment 53 at an intermediate position, both of which are disposed to be engaged by the brush 42 simultaneously with the connecting oi the positive battery with the line through segments 46 and 43 01 ring 36. The ring 36 embodies alternately arranged segments 54 and disposed in similar alinement with the front ends of segments 41 and 49 so as to be contacted by brush 43 simultaneously with the connecting of negative battery through the brush 4| to the line. As will-be seen, this arrangement provides a short segment of contacting material separated by insulating material disposed in alinement with the segments 0! ring 36 at the beginning of each current reversal so that as the current reversal occurs, the

circuit through these segments is completed. The segments 52 and 53 are connected through a common lead 55 and a switch 51 to a' lead 56 :[rom'- the sweep circuit, presently to be described, which is shorted through'the action of these segments.

Segments 54 and 55 are connected throu h com mon lead 59 and switch 6| to the same sweep circuit lead 58 as the segments 52 and53. The

switches 51 and 5| provide means for cutting oi! the action of either pair of segments which, as the description will show, provide means for cutting out either half or the pattern corresponding to either the positive or negative portion or the signal cycle. 1 V

The network 32 is of the bridge duplex type ordinarily employed for ocean cable circuits and comprises ratio arms 62 and 63, including capacitors, as the dividing reactors. The arms areioined at a common point 64 and connected through inductance 65 and conductor '44 to the current reversal brush 4| of the test signal distributor. The real line or cable 30- and the artificial line 31' comprise the other arms of the bridge and are joined respectively to the ratio arms at the conjugate points X and Y across which the receiving apparatus is connected. The apparatus employed for testing according to this invention may be used in connection with any of the usual types of receivers and may be connected across any two pointsin the receiving circuit across which it is desired that no unbalanced potentials occur. The arrangement of receiving apparatus shown is merely illustrative and comprises a series receiving capacitor 66 and a receiver coil 61. The receiving coil may be shunted ii desired by means such as inductance 63 in series with a resistance 69.

The form oi artificial line 3| does not iorma part of this invention. It is to be understood that any type of artificial line may be employed which provides for acflustment of the various elements" constituting the line. A'conventional type of artificial line is illustrated comprising several resistances 1| arranged in series with induetances 12 arranged to simulate the resistance and inductance oi the real line. The capacitance of the real line is simulated by connecting a suit able number of capacitors 13 from suitable points in the resistance-inductance series to ground.

With regard to the amplifier 34 connected bebetween the receiver and the cathode ray tube 33,

the major considerations are that it shall have substantially straight-line amplification characteristics for a wide range of frequencies extending down to substantially zero and also introduce the minimum disturbance into the receiving circuit. The latter of these conditions is largely met, for example, by employing a so-called selfcontained amplifier enclosed within a shielded compartment having no ground connections. By this means the capacity of the amplifier to ground is made negligible, reducing the error which may be thus introduced. A self-contained amplifier is one employing batteries within the shielded compartment for providing the'necessary potentials, thus avoiding any direct or inductive circuit path through the amplifier toground. Special attention is also. given to these lectures in the cathode ray tube and its power supply, as will be presently described An amplifier having substantially fiat amplification characteristics is secured by employing direct coupling between the various stages within the amplifier.

The amplifier shown by way of example comprises 'a pair of electron tubes 14 and 15 direct coupled in cascade. The input to the amplifier is obtained from apotentiometer 16 connected across the receiving coil 61 In accordance with the purposes 01' this invention, as already stated, the potentiometer 15'may be connected across any portion of the receiving circuit where it is desired to determine or eliminate unbalance potentials. The amplifier is iedthrough the'input grid of the first tube 14, which is connected to the arm of the potentiometer 16. The anode of the tube 14 isconnected by means of a suitable conductor directly to the input grid 01' the second tube 15. Operating current at a suitable potential is provided for both the'anode oi the first tube and the grid of the second tube, through a resistor 11. The current to the anode of the secondtubeis'suppliedthrougharesiswrjl. The connection oitheamplifiertothecathoderay tern.. In the drawings, the cathode ray tube is tube is provided through coupling or blocking condensers I9 and 8 I.

The proper current potentials for the various elements of the amplifying tubes are-supplied as illustrated in the drawings from a common battery 82 having a suitable total voltage by tapping the battery at suitable points intermediate its plus and minus ends. Negative bias for the grid of the input tube I4 is preferably supplied by battery 83 having a potentiometer bridge across a portion thereof for suitably adjusting the bias. By employing a battery instead of' a voltage divider supplied with potential by separate source, the possibility of feed back or regeneration which would alter the frequency characteristic of the am plifier is avoided. It will be understood by those skilled in the art that suitable by-pass condensers are employed to provide individual shunt circuit paths for various portions of the amplifier where needed. A potentiometer 84 which is connected to the amplifier side of coupling condenser or capacitor BI is provided to adjust the potential upon that condenser to substantially equal that impressed upon the condenser I0. -In other words, by means of a potentiometer 84, compensation can be made for the averagedrop in potential across the resistance I8 due to the current drawn by the output tube I5.

I In the preferred form of the invention the power supply for the cathode ray tube 03 is speciallydesigned to the capacity. to

ground through the apparatus to eliminateas in connection with the amplifier, any disturbances in the signal circuit from that source. In order to provide for the high potentials required tor a cathode ray tube, it is desirable to supply the. operating potentials from a step-up transformer 81 operating through a suitable tube rectifier 00.-

Without taking special precautions, considerable capacitance would be introduced through the transformer 81. This is avoided by supplying the current to the primary of the transformer from a motor-generator arrangement including a motor 89 supplied from power leads and a generator 9| which is driven by the motor but is electrically insulated therefromand arranged so that. the electrostatic capacity between the motor and generator is negligible.

The cathode ray tube 33 has current supplied at the proper potential for'its various elements from the rectifier 88 by the use of a voltage divider 02 comprising a series of resistance ele-' ments 93, 94, 95, 96 and 91. The cathode and several grids of the cathode ray tube 86 are arranged in a conventional manner and connected to the voltage divider either by tapsor a potentiometer to supply the proper potentials. The

sweep circuit arrangement to be described includes a variable resistance 98 tapped between the voltage divider elements and 06. The cathode ray tube is or a conventional type and ispreierably provided with a special retentive screen by meansof which the patterns developed upon the screen will be retained for a considerable period, such for'example as that described in the abovementioned Du Mont patent.

The cathode ray tube is pro tied with quadrant plates IOI, I02, I03 and I04 for controlling-the deflection of the electron beam in a well known manner. The plates WI and I03 comprise the side to side plates and are employed to produce what is known as the sweep movement of the electron m, .Plates I02 and I04 are'th'e up the beam from the normal ax'isto form the patand down plates andproduce the deflections or resistor 98 and produce a sweep which will be shown diagrammatically and the actual relation- ?p of the plates IOI,-, I02, I03 and I04 is not own.

The sweep of the electron beam is not produced bythesignal asin, the embodiment of Fig. 1 but is produced concurrently with the signal by the control provided through the commutator 55. The plate I03 is preferably connected back from the positive end of the voltage divider midway 10 between the positive end and the point where the variable resistance 08 is tapped.- The opposite plate IOI is normally-connected through the variable resistance and thence to a stilllower point on the voltage divider as already indicated. The .1

sweep is produced by what is known as the variable condenser-resistance method by which the relative potential between plates IOI and I0! is changed from that at the extreme positive end of the voltage divider to that at the point between i" resistance elements 95 and 05 where the-plate is normally connected through the resistance 08 to l the voltage divider. The action of the combined condenser-resistor arrangement, such as illustrated, for producing sweep, is well known in the art. However, ac-

cording to this invention, a special type of control mechanism as already described in connection with commutator 35 is provided for coordinating the action of the sweep circuit with the e signals. The sweep circuit comprises the variable resistance 08 tapped, as already stated,v at a point on; the'voltage divider having a lower potential' than plate I03; and av variable condenser I05. The condenser I05 is connected in the sweep 011'- cuit with one side to the plate I0 I and the other side to the positive end 01' the voltage divider 92.

The special control provides means for periodically short-circuiting condenser I05 in synchronism with the test signals.

It will be seen that short-circuit being established plate IOI will as-; sume the potential'ot the positive or high .end of immediately upon the the voltage divider 02. When the short-circuit is removed, the condenser I05 will begin to charge through the resistance 98, due to the fact that the opposite electrodes of the condenser are then connected to points along the'voltage divider at 1 different potentials.

As the condenser I05 charges'ata rate determined by the capacity o!- the condenser and the value of the resistance -00, the plate IOI tends to assume the potential of the point along the voltage divider at which the lead through the resistance 08 is tapped. Since the point just mentioned, which determines the potential of plate I0 I, when the condenser has become fully charged,-is at a potential lower than plate I03, and the positive end of the voltage more nearly linear with time than that obtained with a simple resistor as shown.

The vertical .plates l02 and I04 derive their normal potential from the positive end of the voltage divider through a common resistor I00,

and individual resistors I01 and I08. The up and down potentials are impressed upon the plates from the amplifier 34 through the coupling condensers I9 and 8|. plates I02 and I04 is direct to these condensers,

so that the potentials transmitted by the latter free or floating. At the same time the leakage through the resistors I01 and I08 tends to maintain them at the same potential at no load, and the leakagethrough the resistor I08 to the voltage divider tends to maintain them at the desired elevated potential with respect to the other elec- The connection from the between the real and artificial lines, the operation of the -various parts when test signals are applied will now be described. In order for a substantially stationary pattern to appear upon the screen of the cathode ray tube, a control of the sweep circuit must be provided. In this embodiment of the invention means is provided for causing complete traverse of the electron stream, or the light spot upon the screen, for each half cycle of 'the signals impressed upon the duplex circuit. Particular attention is drawn to what is accomplished by such a coordination of the sweep circuits with the signals. As is well recognized, the propagation of each signal along a transmission -line requires an appreciable and measurable time period. If a control of the sweep circuit of the cathode ray tube is provided to coordinate itsaction with the origination of the signals, so that the pattern forming a portion of the spot travel is'started at'a certain point in each signal cycle or half cycle, and progresses across the screen in the usual manner at a steady rate, the movement of this light spot provides a "scale of measurement for the propagation of the signals during each cycle. In other words, if the light spot is swept across the screen for each reversal of the signal current, elemental lengths --produced by a traverse of the light spot for each able to followthrough the origin and propagation of a full current reversal or signal cycle and I,

the coordination of the sweep circuit thereto. As will be seen, the alternate segments of the ring 36 of the commutator are connected to opposite polarities, the segment 48 being coupled to the positive side of the battery II, and the segment 41 to the negative side of battery SI. Therefore, when the brush 4I sweeps the commutator, the head of the duplex circuit will be connected through conductor 44 first to positive and then to negative battery. The frequency of the signals, or the speed of the reversals, may be made any desired value by adjusting the speed of the brush arm 30. Assuming that the brush begins to rotate as soon as the bridge 32 is connected to positive battery, a current charge quickly divided between arms 82 and 83, rushes into the real line 30 and the artificial line 3|. The capacities near the head of the respective lines take up a considerable amount of current rapidly. However, capacities away from the head of the real and artificial lines take up' current more slowly, so that a signal wave is propagated along the lines at a rate determined by the line 'reactances. As is well understood, these reactances may be comprised of capacitance. which in ocean cables is the primary factor, and resistance or inductance. In a duplex circuit, the artificial line is intended to simulate these values throughout the length of thereal line. When discrepancies between the reactance values of the real and artificial lines are present, an unbalance exists, and in accordance with the operation of duplexed circuits, the signal current will not be equally divided between the real and artireceiving devices will occur.

As the commutator started to rotate brush 42 engaged segment 52, which is connected to the lead 58 extending from one side of the sweep control circuit. The brush 42 being connected with lead 45 from the other sideof the sweep control circuit, the circuit is closed momentarily and the condenser I05 is short-circuited by the passage of the brush section over the commutator segment 52. The width of the segment 52 is made small so that the circuit is closed only momentarily. This, however, discharges the condenser I05 and causes the-deflector plate IOI of the cathode ray tube to assume the voltage at the positiveend of the voltage divider 82. This i suddenly brings the light spot on the screen to the extreme left position.

Segment 54 on the commutator also connected to the lead 58 is so positioned that the brush 43,

also connected to lead 45, closes the sweep circuit by contactingthe segment just at the time that the reverse current through the segment 41 is impressed upon the signal circuit. The other two segments 53 and perform the same functions with respect to the signal reversals occurring as the current from the segments 48 and 48 is impressed upon the signalcircuit.

As the brush leaves the segment 52, the

' sweep control circuit is again opened and the charging of condenser I05 through resistance 88 moves the spot-to the right relatively slowly, at a speed determined by theadju'stments and values of the capacity I05 and resistance 80. The

range of thevalues'and adjustments are preferably such that the spot of light can be made to travel across the screen within a time approximately equal to the full period of each half cycle of the signal or within a shorter time, period when it is.desired. when the. spot is adjusted to travel at a shorter time period, it means that.

the pattern represents not the entire half cycle of the signal but some predetermined portion thereof. v

With the sweepcircuit control segments 52, 53, 54 and 55 in the position shown with, respect to the signal segments 46, 41, 48 and 49, the light spot will be brought to a starting point at the beginning of each signal reversal. If it is made to travel across the screen within a period which represents a fraction of each signal half cycle, it will mean that the pattern will represent the portion of the signal cycle first impressed upon the line and will be a picture of the unbalanced condition existing in the portion of the real and artificial lines which the signal first penetrates; or in other words, the near or the head ends of the respective lines. 1 Therefore, by this means the screen pattern maybe made to give an enlarged picture of the unbalance currents in a' desired fractional portion of the line extending out from the head end.

The double pointed arrow placed near the commutator ring 36 is intended to indicate that this ring may be adjusted rotationally with respect to rings 31 and 38 carrying the sweep circuit control segments. By means of adjustment of ring 36 such that the sweep circuit control of sho'rt-circuiting segments are positioned at points later in the half cycle current reversal periods and enlargement of the unbalanced conditions of any section of the artificial and real lines may be pictured. By suitably continuing the adjustments, the entire extent of the signal circuits and the relation between the real and the artificial lines may be explored insections.

As has already been pointed out in connection with the previous embodiment, the portions of the pattern representing the opposite half; cycles of signal current propagation-are represented by similar defiections in opposite directions from capacity placed at evenly spaced distances,

the light s a zero axis. Aswill be presently pointed out in connection with tracings of actual screen patterns produced by the embodiment of this invention shown in Fig. 10, the switches 51 and! in the sweep circuit control leads and the corresponding commutator arrangement permit the portion; of the pattern resulting from either the positive or negative half of the signal cycle to be produced separately.

To interpret the meaning of the screen patterns and the manner in which they are employed in a method of rapidly balancing duplex circuits of every kind including particularly long ocean cables, tracings of a number of typical patterns are illustrated in the drawings in Figs. 11 to 15. Certain of these tracings are produced by a known set of conditions and by this means a system of reading or interpreting the tracings is developed.

Referring now to Fig. 11, which'includes several tracings produced by a series of known con-, ditions, tracing K is of a screen pattern produced by the insertion of excess capacity at the head, of the artificial line. It will be noted that there is a deflection of the beam above and below the horizontal axis immediately at the beginning of t sweep. Tracing L represents a patternproduced when this capacity is moved a short distance back from the head of the artificial line. Tracings M, N and represent the conditions when the excess capacity is progressively moved farther out on the artificial line. The relative positions of the humps of the. pattern for excess capacity occurring at different distances in the artificial line, will not be the same for all artificial lines. .The positions or the excess capacity can be fairly accurately determined and calculated, however, by close measurements of the patterns with a test excess ginning at the head,of the artificial line and continuing to the extreme outer end thereof. Thusit will be apparent that by employing the method and apparatus of the invention as herein described, a quick and accurate determination of the position in artificial line where the inequalities lie may be made. As will be pointed out, the shape of the unbalance pattern further artificial line so that the necessary correction may be made, and by employing sufiicient amplification, the balancing may be carried out to any desired degree of refinement.

Referring to Fig; 12, tracing P shows a pattern in which there is a capacity unbalance at two points in the artificial line. This tracing shows a pronounced deflection adjacent thehead of the artificial line and a similar deflection at a point back from the head of the line.

The tracing Q represents one half of the pattern shown by the tracing P and is obtained by opening one of theswitches 51 or 6| which limits the sweep of the cathode beam to only one of the half cycles. By a test placement of a capacity in the artificial line with one half of the cycle represented in the pattern it is easy to determine the direction of the deflections representing an excess of capacity in the artificial line. Assuming that an upward deflection in tracing Q represents an excess, it will be seen that there is too much capacity adjacent the head of the artificial lineand too little capacity at apoint back from the head end.

By utilizing the method of operation illustrated in the tracing Q, the position and direction of any unbalance in the artificial line may be easily. ascertained. By combining both halves of the pattern as shown in tracing P as well as the previous, tracings illustrated in Fig. 11, slight amounts of unbalance can be more easily distinguished because of the fact that the two halves of the tracing separate from each other by a distance double the amount of the deflection. This advantage will be most appreciated in making the final adjustments which are usually of very small quantities as the refinement of the \balance proceeds.

Fig. 13 illustrates tracings unbalance is primarily in the nature of unequal resistance in the artificial and real lines. It will be seen that the tracings R and S are composed of two parts which cross each other and are separated and in substantially parallelism adjacent produced when the the remote end. The portion of the artificial line in which the resistance unbalance occurs will be round to correspond with the point at which these tracings cross each-other on the zero axis.- The amount of resistance unbalance will correspond substantially to the amount of separation of the parallel portion of the tracings.

when there is a resistance unbalance there niay,also be present capacity or inductive unbalance. as .well. a condition. In order to establish a balance the best procedure would be to eliminate the'capacity unbalance by adjusting the portion of the artificial line corresponding in this instance to the two nodeson "the pattern adjacent the head of the line. After this unbalance has been cleared up, the patterns will cross each. other as shown ance can be located.

The, tracing T representssuch In ,Fig. 14 is illustrateda series of tracings of actual patterns or graphs obtained while balancing anocean cable in actual service'by the First,

method and apparatus described above.

the pattern U was obtained which indicated at least three points of capacity unbalance. The sense and direction of these was established by cutting out one half of the pattern which gave the tracing V and following the analysis just explained in connection with tracing Q of Fig. 12, the tracing V indicates a deficiency of capacity adjacent the head of the artificial line and too great a capacity at a point slightly removed from the head with a second point of deficiency a little further along. After making a small number of adjustments in comparison with the adjustments ordinarily required to greatly improve the balance of a cable, the tracing W was obtained.

The tracings U, V and W were obtained with a circuit arrangement substantially as shown in Fig. 10 in which the amplifier .employed between the cathode ray tube and the circuit across which it was desired to establish a balanced condition was adjusted to a low value in order to bring the unbalance pattern within the confines of the screen of the cathode ray tube. After the adjustments had been made and the tracing W obtained, the amplification was increased which resulted in the tracing X. It will be noted by comparing tracing X with W that the wide portions of the tracing W have now become sepaarted into half cycle pattern portions in X. With the amplified pattern as a guide, the refinement of the cable balance was continued to a point that had never been approached heretofore.

The method of balancing according to the invention has the further advantage, when utilized in connection with signalling circuits or cables subject to outside interference, that the disturbances or parasitic currents thus produced in the circuit may be recognized and eliminated from consideration. In the past, the presence of such currents greatly complicated the balancing operation, particularly in ocean cables of great length where the parasitic currents are large compared with the signalling currents.

This feature of the invention may be explained in connection with Fig. 15, in which tracing Y represents a symmetrical unbalance pattern obtained with the apparatus of Fig. 10 with no interference on the circuit. If a parasitic current, such as indicated in tracing Z is flowing through the signalling circuit, the pattern obtained will be of the form shown in the tracing YZ. The envelope of the pattern has the same form as the pattern Y and thus the character and amount of unbalance is still evident even through the interference current is of greater amplitude than the unbalance current. If as is usually the case, the interference current is not periodic, as shown in tracing Z, but merely consists of intermittent spaced impulses, it causes an unsymmetrical distortion of the unbalance pattern and thus may be readily recognized since the unbalance is always represented by a symmetrical pattern.

In actual practice it may be desirable to observe or correct the balance on a signalling circuit while it is in use, the transmitting current impulses being utilized instead of applying testing current to the circuit as described in connection with the embodiments shown in Figs. 1 and 10. Reception from the remote end of the circuit must, of course, be discontinued during this operation.

The apparatus may consist of relays arranged to control the sweep of the light spot in the cathode ray tube in such a manner that the spot is returned to its starting position jus before each reversal of the cable. Then during the signal impulse the unbalance pattern is traced as described above. Fig. 16 illustrates by way of example control relays I25, I26 and I2! of the polarized type arranged to control the sweep circuit of a cathode ray tube I28 provided with pairs of control electrodes I29, I30 and I3I, I32. The connection of amplifier I33 and cathode ray tube I28 to the duplex circuit I34 of the bridge type is the same as that shown in Fig.10 and already described in detail. The usual transmitting key is indicated at I35. From the foregoing description of the embodiment shown in Fig. 10, it will be evident that unbalance patterns of the type illustrated in Figs. 11-15 will be formed by the tube I28 if the sweep circuit condenser I36 is short-circuited in properly timed relation to the reversals in the cable effected by the key I35. The condenser I36 is charged from the supply circuit of the cathode ray tube through the variable resistor I31 corresponding to the resistor 98 of Fig. 10.

The main line windings of the polar relays I25, I26 and I2! are connected in series relation across the key I35 so that the current traversing these windings is reversed each time the key is operated. Since the armatures of relays I25 and I26 are connected together and the front and back contacts, respectively, of each of these relays are connected in parallel and to opposite sides of the condenser I36, it will be apparent that a momentary short-circuit will be placed across the condenser if the relays operate at different speeds, i. e., if the armature of one relay engages its lower contact before the armature of the other relay disengages its upper contact or vice versa.

In order to effect this result, a biasing current derived from a battery I38 is applied to the lefthand accelerating windings of relays I25 and I26, the windings being connected in opposite series relation. The strength of the biasing current and hence the duration of the short-circuit across the condenser I36 may be adjusted by resistor I39.

The short-circuit of the sweep circuit condenser I36 should take place at the beginning of the cable reversal. The relay I2! is provided to control the timing of the short-circuiting operation and, in order to accomplish this result, it is arranged tosend a biasing current through the central or opposing windings of relays I25 and I26. The contacts of relay I2'I,are connected to opposite ends of battery I38 and the opposing windings of relays I25 and I26 are connected to the armature of relay I21 and a midpoint tap on the battery I38 so that the biasing current is reversed upon each operation of relay I21. The circuit of the opposing windings of the relays includes a variable resistor I40 which controls the timing of the short-circuit of condenser I36 with respect to the cable reversals and hence the instant when the cathode ray beam is returned to its starting position to commence another trace. By proper adjustment, the shunting of the condenser may be caused to take place before the sending-on relays operate and before zero current is reached in the cable.

In this manner a momentary contact is obtained in timed relation to the cable reversals for controlling the sweep circuit of the cathode ray Many other modifications will occur to those a skilled in the art and may be made without departing. from the scope of the invention which 2,1sc,coc

involves a radical departure from the prior practice. Heretofore balancing of lines, particularly long cables where an extremely accurate balance is desirable, has been a tedious, cut-and-try procedure requiring experienced highly skilled workers. The method and apparatus embodying the invention on the other hand lead to improved results which are obtained more easily and expeditiously. The balance may be refined to any extent desired and the effect of any balancing adjustment is immediatelymade apparent. The apparatus is so sensitive that the efiects of obscure unbalances caused by the characteristics of terminal equipment or other causes can be discovered and compensated. In general a better balance can be secured and maintained which is of the utmost importance, for'example, in long cable circuits since higher speeds of transmission may be employed, thereby increasing the line capacity without substantially affecting the plant equipment or operating expense. Many other instances might be cited to. show the utility and value of the invention in particular applications.

I claim:

1. The method of balancing acircuit and an artificial line which consists in impressing cyclic current impulses on said circuit and artificial line, forming a time-current graph or pattern of at least a portion of the unbalance current during each impulse and making successive balancing adjustments in the artificial line concurrently with observations of the resultant changes in the graph or pattern to reduce the magnitude of the unbalance between, the circuit and the artificial line.

2. The method of analyzing unbalanced conditions in a duplex circuit which consists in impressing cyclic current impulses on the real and artificial lines thereof and forming a time-current visible pattern of at least .a portion of each impulse of a character representing the relation between the current propagation in the real and artificial lines in which difierences in current appear as displacements from a reference axis of the pattern.

3. The method of comparing circuits or other electrical elements which comprises subjecting the same to an electrical potential, balancing the currents flowing during an appreciable time interval and representing the difierence or unbalance current at successive instants during said time interval in a form in which the magnitude, time and direction of any portion of such unbalance current maybe observed.

4. The method of comparing circuits or other electrical elements which comprises subjecting the same to cyclic current impulses, balancing the currents flowing to each element and forming a sustained visible time-current graph or pattern of the unbalance current flowing during each cycle.

5. The method of balancing a circuit which comprises superimposing a visible time-current graph or pattern of the unbalancev current after making balancing adjustment upon the graph ,rent impulses and forming a symmetrical timecurrent pattern of the unbalance current whereby the parasitic currents flowing through the circuit and forming an unsymmetrical pattern may be segregated from the unbalance current in analyzing the pattern.

'7. The method of balancing a circuit subject to either periodic or aperiodic interference which comprises subjecting said circuit to potential to cause a current; wave propagation through the circuit and forming a time-current pattern of the unbalance and-interference current in such form that the unbalance may be segregated from the periodic or aperiodic interference.

8. The method of balancing a duplex circuit which comprises forming a graphic pattern of the cyclic unbalance current in which the unbalance is indicated as deflections from a zero axis, making as may be indicated by concurrently observing the changes in the pattern such successive balancing adjustments in the artificial" line as tend to cause the deflection lines of the pattern to approach the zero axis, and at a plurality of stages in the procedure amplifying by successively greater amounts the deflections as the balance is refined.

9. The combination of a duplex circuit-having a real line and an artificial line, and means including a cathode ray tube forforming a significant time-current pattern continually indicating the condition of balance between said real line and artificial line whereby the efiect of balancing adjustments of the circuit become immediately apparent.

10. The combination of a duplex circuit having a real line and an artificial line, a cathode ray tube of the fluorescent screen type provided with control elements, connections between said control elements'and said circuit, means to provide v an artificial line, of luminescent means for forming a sustained visible pattern representing the character of the unbalance between said conductor and said artificial line.

12. The combination with a line conductor and an artificial line, of electro' responsive means for forming a visible pattern representing the character of the unbalance between said conductor and said artificial line and for superimposing thereon a visible pattern representing the character of the unbalance after a balancing adjustment has been made. i

13. The combination with a line conductor and an artificial line, of means for propagating current waves over said line conductor and said artificial line and means including a cathode ray tube 'for indicating the relation between the current flow in said conductorand that in said artificial line in a form in which the parasitic currents to which said conductor may be subject may be distinguished from the unbalance current.

14. The combination with a line conductor and an artificial line, of means for propagatingcurrent waves over said line conductor and said artiflcial line and means including a cathode ray tube for indicating the time-current relation beween the current waves in said line conductor and said artificial line, respectively.

15. The combination with a line conductor and an artificial line, of means to apply current impulses to said'conductor and said artificial line,-

and means including a cathode ray tube for indicating unbalance between said conductor and said artificial line, said last-mentioned means further comprising a sweep circuit for said tube and means for energizing the same in synchronism with said current impulses.

16. The combination with a line conductor and an artificial line, of commutator'means to apply successive current impulses to said conductor and said artificial line and means including a cathode ray tube responsive to said impulses for indicating unbalance between said conductor and said artificial line, said' tube being provided with a sweep circuit connected to said commutatormeans to be energized in synchronism with said current impulses. V

17. The combination with a line conductor and an artificial line, of transmitting equipment for signaling over said conductor and means including a cathode ray tube responsive to signaling impulses for indicating unbalance between said conductor and said artificial line whilethe conductor is in use, said means further comprising a sweep circuit for said tube and relay means for conditioning said sweep circuit in timed relation .to .said signaling impulses.

18. The combination with a line conductor and an artificial line, of a cathode ray tube unbalance indicator having control elements connected to said line conductor and artificial line and an adjustable-gain amplifier interposed between said conductor and said unbalance indicator.

19. The combination with a line conductor and an artificial line, of means for applying cyclic current thereto and means for forming a pattern representing the character of the unbalance between said conductor and said artificial line, said last-mentioned means including a cathode ray tube provided with a luminescent screen and means for sweeping all or a part of each cycle of current over the entire width of the screen of said tube.

20. The combination with a line conductor and an artificial line, of means for applying current impulses thereto and means for forming a pattern representing the character of the unbalance between said conductor and said artificial line, said last-mentioned means including a cathode ray tube and means to sweep the cathode ray beam of the tube in timed relation to said impulses and at a non-uniform rate depending upon the rate of propagation of the impulses in said line conductor and artificial line.

21. The combination with a line conductor and an artificial line, of means for applying current impulses thereto and means for forming a pat-v tern representing the character of the unbalance between said conductor and said artificial line, said last-mentioned means including a cathode ray tube and means forproducing a sweep of the cathode 'ray beam of the tube at a uniform rate independent of the rate of propagation of the current impulses insaid line conductor and artificial line.

22. The combination with a line conductor and an artificial line, of means for forming a pattern representing the character of the imbalance between said conductor and said artificial line, said means including a cathode ray tube, means for deflecting the cathode ray beam of said tube along the coordinates of the screen and means for enlarging the amplitude of the deflection of the beam along either or both of said coordinates.

23. The combination with an electrical circuit having variable electrical constants and means for impressing signalling current thereon, of means comprising a cathode ray tube connected to said circuit for providing a visual indication of any departure from optimum adjustments of said circuit in response to the fiow of current therein.

24. The combination with signal receiving apparatus including an electrical circuit, an electrical constant of which is variable, of means comprising a cathode ray tube for indicating the required adjustment of said circuit for optimum receiving conditions.

25. The combination with a line conductor and an artificial line having distributed capacity and line coil and a cathode ray tube having sweep plates connected across the line coil and deflection plates connected across conjugate points of the bridge.

28. The combination with a duplex circuit of a cathode ray tube provided with'a sweep circuit and an unbalance deflection circuit, connections between said deflection circuit and said duplex circuit, and means for timing or conditioning current flow in said sweep and unbalance deflection circuits.

29. The combination wtih a-line conductor and an artificial line, of means for applying positive and negative signals thereto and means for observing the unbalance between said conductor and said artificial line in response to only the positive signals or only the negative signals as desired.

30. The combination with a line conductor and an artificial line, of means for forming a visible pattern representing the character of the unbalance between said conductor and said artificial line, said means comprising a cathode ray tube having a screen and control means to sweep the cathode ray beam with alternate halt cycles of signalling current represented on opposite sides of an axis transverse to the line of sweep on the tube screen.

31. The combination with a line conductor and an artificial line, of means for forming a visible pattern representing the character of the unbalance between said conductor and said artificial line,- said means including a cathode ray tube. having a screen'and means for sweeping the cathode ray beam from one side of the screen to the opposite side for each half cycle of sig-,

nalling current with positive and negative signalssymmetrically arranged with respect to the sweep axis on said screen. I

32. The combination with aline conductor and an artificial line, of means for forming a visible pattern representing .the character of the unbalance between said'conductor and said artificial line, said means including a cathode ray tube having a screen and a shielded self-contained ungrounded straight-line amplifier interposed between said tube and the conjugate points of said line conductor and artificial line.

33. The combination with a line conductor and an artificial line, of means for forming a visible pattern representing the character of the unbalance between said conductor and said artificial line, said means including a cathode ray tube having a screen and means for producing a sweep of the cathode ray beam of said tube in response to each successive signal applied to the line conductor and artificial line.

34. In an electrical communication system. means for transmitting signalling variations, receiving means for said variations including an adjustable receiving circuit containing inductance and capacity and means including a cathode ray tube connected to said receiving means in a manner to be affected by the characteristics of said receiving circuit to facilitate the adjustment of said circuit for optimum reception.

WILLIAM D. BUCKINGHAM. 

